1. Technical Field
The disclosure relates to energy storage devices and in particular to a method of operating a sodium metal halide electrochemical cell.
2. Discussion of Art
Work has been done on rechargeable batteries that use sodium as the negative electrode. Sodium has a standard reduction potential of −2.71 volts (V), is relatively low weight, non-toxic, abundant, and economically desirable in the form of sodium chloride. The sodium anode can be used in liquid form, and the melting point of sodium is 98° Celsius (C.). An ion conducting solid electrolyte (separator) separates the liquid sodium anode from a positive electrode (cathode).
The cathode includes a material that can be oxidized/reduced upon charging/discharging the cell. Within the cathode, a liquid electrolyte transports ions to and from the separator on the cathode side. The sodium-ion conductivity of the two electrolytes, determines the minimum operating temperature of the battery. In the case where the liquid electrolyte is a molten salt, the melting point of the salt determines the minimum temperature.
U.S. Pat. No. 5,006,427 to Böhm et al, is directed to a storage battery. Böhm et al. express concerns regarding thermal overloads in the cells and disclose that an object of their invention is to construct cells of a battery in such a manner that uniform cooling of the cell is realized with low expenditures of energy for cooling and a minimal temperature gradient within the cells, with a simple battery configuration having simple interconnections.
US Patent Publication No. 2009/0169990 to Gardner et al. is directed to a battery design with asymmetrical terminals. The cell includes a plurality of electrode sheets separated by at least one separator sheet. A positive extension tab is attached to current collecting tabs of positive electrode sheets, and a negative extension tab is attached to current collecting tabs of the negative electrode sheets. The dimensions of the positive extension tab and the negative extension tab are selected such that temperature difference between the positive extension tab and the negative extension tab are minimized when the electrochemical cell is in use.
There is a continual desire in the industry to improve the power capability, energy content, cycle life, and/or calendar life of energy storage devices.